Tank-venting systems having the following features are known for a long time:
an adsorption filter having a venting opening at its venting end and a connecting line to the tank; PA1 a tank-venting valve which is connected into a connecting line between the intake pipe of the engine and the intake end of the adsorption filter; and, PA1 a drive unit for the tank-venting valve. PA1 a difference pressure is measured which is a measure for the pressure difference between the venting end and the intake end of the adsorption filter; and, PA1 a conclusion is drawn as to inadequate throughput of the adsorption filter when the measured difference pressure exceeds a threshold value. PA1 the tank-venting valve is closed after a regeneration phase of pregiven duration has run wherein an underpressure has developed in the tank-venting system and a difference pressure (Dp) is measured essentially when closing the tank-venting valve with this difference pressure being a measure for the pressure difference between the venting end and the intake end of the adsorption filter; PA1 the time constant .tau. for the decay of the measured pressure difference is determined after closing of the tank-venting valve with the aid of at least one further difference pressure measurement; and, PA1 a conclusion is drawn as to inadequate throughput capacity of the adsorption filter when the determined time constant is longer than a threshold value time constant (.tau..sub.-- SW). PA1 a determination is made as to whether tanking takes place; PA1 in the event that tanking is determined, the difference overpressure (Dp) is measured which corresponds to the difference between the inner pressure of the tank-venting system and the ambient pressure; and, PA1 the tank-venting system is evaluated as being clogged when the measured difference overpressure exceeds a difference overpressure threshold value (Dp&gt;DSP.sub.-- SW). PA1 a difference pressure sensor for measuring a difference pressure which is a measure for the pressure difference between the venting end and the intake end of the adsorption filter; and, PA1 an evaluation device which receives the signal from the difference pressure sensor and is so configured that it emits a fault signal which indicates inadequate throughput capacity of the adsorption filter when the measured difference pressure exceeds a threshold value. PA1 a difference pressure sensor for measuring a difference pressure which is a measure for the pressure difference between the venting end and the intake end of the adsorption filter; PA1 a determination device which receives the signal from the difference pressure sensor and, additionally, a signal which indicates closure of the tank-venting valve and which is so configured that it determines the time constant of the decay of the measured difference pressure after closure of the tank-venting valve with the aid of the difference pressure signal supplied to the determination device; and, PA1 an evaluation device which receives the signal from the determination device and which is so configured that it emits a fault signal which indicates inadequate throughput capacity of the adsorption filter when the determined time constant exceeds a threshold value. PA1 a difference pressure sensor (18.2) for measuring a difference overpressure (Dp) which is a measure for the pressure difference between the inner pressure of the tank-venting system and the ambient pressure; PA1 a determination device (25) for determining whether tanking is taking place; and, PA1 an evaluation device which is so configured that it evaluates the tank-venting system as being clogged when, in the case of tanking, the measured difference pressure exceeds a difference overpressure threshold value (Dp&gt;DSP.sub.-- SW).
The drive unit drives the tank-venting valve in a fixed pregiven time pattern, for example, the drive unit alternately holds the valve closed for 1.5 minutes and then opens the valve for 4 minutes in order to make a regeneration of the adsorption filter possible. The opening cross section of the tank-venting valve is determined via a pulse-duty factor dependent upon the particular operating state of the engine.
It is apparent that tank-venting systems of this kind can only then operate completely satisfactorily when they are tight and when the tank-venting valve opens and closes properly. Various methods are known for checking the tightness and the operability of the tank-venting valve. However, it has been shown that these methods are not adequate in order to satisfactorily consider all aspects with reference to the operability of the tank-venting system.
Accordingly, the problem is present to provide a method and an arrangement with which a tank-venting system can be checked differently than previously with respect to operability.